As compared to incandescent lamps, other types of light emitting elements are available that have certain advantages. For example, light emitting diodes (LEDs) can provide a light output comparable to an incandescent lamp but at a significantly improved energy efficiency. Additionally, the lifetime of an LED lamp can be substantially longer than an incandescent lamp.
LEDs can also be configured in a lamp that includes a threaded base (sometimes referred to as an “Edison base”) making it interchangeable with conventional incandescent lamps. Optical elements can also be provided that, in addition to light scattering, can provide an LED-based lamp with a shape similar to that of conventional incandescent lamps. The color and intensity of light provided by the LED-based lamp can also be similar to incandescent lamps.
However, lamps based on solid state light emitting sources such as LEDs typically require operation at relatively low temperatures for device performance and reliability reasons. For example, the junction temperature for a typical LED device should be below 150° C. and in some LED devices should be below 100° C. or even lower. At these low operating temperatures, radiative heat transfer to the surrounding environment is weak compared with that of conventional light sources.
With LED light sources, the convective and radiative heat transfer from the outside surface area of the lamp or luminaire can be enhanced by the addition of a heat sink. A heat sink is a component providing a large surface for radiating and convecting heat away from the LED devices. In a typical design, the heat sink is a relatively massive metal element having a large engineered surface area, for example, by having fins or other heat dissipating structures on its outer surface. Where equipped with a large surface area, the heat fins can provide heat egress by radiation and convection.
However, even with the use of a heat sink, significant challenges remain for sufficient heat dissipation from the lamp. For example, depending upon the amount of light intensity desired, multiple light emitting devices such as LEDs may be desirable. Depending upon e.g., the number of such light emitting devices that are employed, the heat sink alone may not be able to adequately dissipate heat from the lamp through passive means. While increasing the size of the heat sink could improve the dissipation of heat, such may be undesirable because it may cause the overall size of the lamp to exceed specification for form such as e.g., the ANSI A19 profile.
Additionally, some light emitting devices have directional limitations that also present challenges for lamp design. For example, LED devices are usually flat-mounted on a circuit board such that the light output is substantially along a line perpendicular to the plane of the circuit board. Thus, a flat LED array typically does not provide a uniformly distributed omnidirectional light output that may be desirable for many lamp applications. Achieving the desired omnidirectional light distribution thus requires specialized optics that incur a significant penalty in light loss in order to spread the light evenly.
Another challenge relates to aesthetics. A lamp designed only with consideration of performance requirements regarding light output, energy usage, thermal management, etc. may not provide an appearance that is pleasing to e.g., certain consumers. Such can affect the marketability of lamp even if it otherwise performs well.
Accordingly, a lamp that can have improved energy efficiency over traditional incandescent lamps while providing a comparable or better light intensity distribution would be beneficial. Such a lamp that can also be provided with one or more features for providing sufficient heat dissipation where heat generating light emitting elements such as e.g., LEDs are employed would also be very useful. Such a lamp that can also be provided with aesthetically acceptable features would also be beneficial.